1. Field of the Invention
This invention relates to improving the injectivity of a micellar dispersion containing wax in the hydrocarbon phase. Secondary and tertiary-type processes are applicable with this invention as well as stimulation techniques.
2. Description of the Prior Art.
Micellar dispersions are known in the art to be useful for stimulating wells (U.S. Pat. Nos. 3,467,188 to Gogarty and 3,467,194 to Kinney et al). These dispersions are also known to be useful in secondary and tertiary recovery processes, see U.S. Pat. Nos. 3,254,714 to Gogarty et al, 3,497,006 to Jones et al, and 3,506,071 to Jones. The micellar dispersions generally contain water, hydrocarbon, surfactant (preferably a petroleum sulfonate) and optionally cosurfactant (also identified as a cosolubilizer, semi-polar organic compound, etc.), and/or electrolyte. The micellar dispersion can be oil-external or water-external and can contain additives in addition to those mentioned above.
Pertinent patents in the art include:
U.S. Pat. No. 2,193,499 to Carr removes wax deposits from reservoirs by treating the reservoir with a composition containing calcium petroleum sulfonate and a branched chain paraffin.
U.S. Pat. No. 3,670,819 to Dauben stimulates water injection wells by treating the well with a micellar solution slug followed by a "primary" oil-external micellar solution (contains less water than the first micellar solution slug and can contain solvents such as kerosene, organic naphtha, ketone, or carbon disulfide) and this, in turn, followed by a micellar slug of increased water content.
U.S. Pat. No. 3,682,249 to Fischer et al teaches the inhibition of wax from a wax-containing micellar dispersion by incorporating therein about 5-10,000 ppm of a copolymer of ethylene and a monoethylenically unsaturated ester. The copolymer also improves the filterability and injectivity of the micellar dispersion in a porous media.
One of the problems with wax in the micellar dispersion is that once the micellar dispersion is cooled, e.g. in storage or while it is being pumped to the injection site, and then reheated for injection, the insoluble wax crystals that form during the cooling cycle tend to "block" or "plug" the subterranean reservoir rock as the dispersion is injected therein. These wax crystals do not immediately go back into solution when the micellar dispersion is heated. This adverse effect is apparent even if the micellar dispersion has been filtered at high or low temperatures prior to injection. Applicants' incorporation of the low molecular weight paraffin hydrocarbon into the micellar dispersion overcomes the adversity caused by the wax. As a result, the micellar dispersion can be subjected to cooling without experiencing adverse injectivity rates. That is, a micellar dispersion can be made up and filtered at relatively high temperatures, thereafter cooled to relatively cold temperatures as it is pumped to the well head, and then reheated to reservoir temperatures as it is pumped from the well head down to the reservoir rock without adverse injectivity problems. the low molecular weight paraffin can be added to the micellar dispersion before this cooling and heating cycle.